The invention relates to a gas and steam turbine plant with a heat recovery steam generator which is located downstream of a gas turbine on the flue-gas side and the heating surfaces of which are connected into the water/steam circuit of a steam turbine, and with a fuel gasification device located upstream of the combustion chamber of the gas turbine via a fuel line.
A gas and steam turbine plant with integrated gasification of fossil fuel conventionally includes a fuel gasification device. The gasification device is connected on the outlet side to the combustion chamber of the gas turbine via a number of components provided for gas purification. The gas turbine heat recovery steam generator, the heating surfaces of which are connected into the water/steam circuit of the steam turbine. A plant of this type is known, for example, from UK Patent Application GB-A 2 234 984.
Furthermore, German Published, Non-Prosecuted Patent Application DE 33 31 152 A1 discloses a method for operating a gas turbine plant combined with a fuel gasification plant. In this case, nitrogen can be supplied to the fuel gas directly upstream of the combustion chamber.
In this plant, a saturator is connected into the fuel line between the gasification device and the combustion chamber of the gas turbine. In the saturator, the gasified fuel is laden with steam. Such a plant reduces pollutant emission during the combustion of the gasified fossil fuel. For this purpose, the gasified fuel flows through the saturator, countercurrent to a water stream. The water stream is carried in a water circuit designated as a saturator circuit. For especially high efficiency, heat can be fed from the water/steam circuit into the saturator circuit.
By coming into contact with the heated water stream in the saturator, which is carried in the saturator circuit, the gasified fuel is saturated with steam and to a limited extent undergoes heating. In this case, for thermal and also operational reasons, further heating of the fuel may be necessary before the fuel is supplied into the combustion chamber of the gas turbine.
It is accordingly an object of the invention to provide a gas and steam turbine plant that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that has especially high plant efficiency.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a gas and steam turbine plant. The gas and steam turbine plant includes a gas turbine, a steam turbine, a heat recovery steam generator, a heat exchanger, and a mixing device. The gas turbine has a flue-gas side and a combustion chamber. The steam turbine has a water/steam circuit. The heat recovery steam generator is located downstream of said gas turbine on said flue-gas side. The heat recovery generator has heating surfaces connected into the water/steam circuit of said steam turbine. The heat recovery steam generator has a fuel gasification device located upstream of the combustion chamber of the gas turbine on a fuel line. The heat exchanger has a primary side and a secondary side connected on the primary side into the fuel line between the gasification device and a saturator. The heat exchanger connects on the secondary side into the fuel line between the saturator and the combustion chamber. The mixing device admixes nitrogen in the fuel line between the heat exchanger and the saturator.
In accordance with another feature of the invention, the gas and steam turbine plant includes a crude-gas heat recovery steam generator upstream of the saturator. The crude-gas heat recovery steam generator precedes the heat exchanger in the fuel line.
In accordance with another feature of the invention, the gas and steam turbine plant includes a further heat exchanger. The further heat exchanger has a primary side and a secondary side. The secondary side of the further heat exchanger connects into the fuel line between the saturator and the combustion chamber.
In accordance with another feature of the invention, the further heat exchanger is heated by feedwater.
In accordance with this object, a heat exchanger is connected on the primary side into the fuel line between the gasification device and the saturator, in addition to a mixing device for admixing nitrogen, and is likewise connected on the secondary side into the fuel line between the saturator and the combustion chamber.
In a plant of this type, the admixing of nitrogen to the gasified fossil fuel, also designated as synthesis gas, is intended for maintaining particularly low NOx limit values in the combustion of the synthesis gas. The mixing device provided for admixing the nitrogen is connected into the fuel line upstream of the saturator on the fuel side. The heat exchanger is, in this case, connected into the fuel line upstream of the mixer and saturator on the primary side and downstream of the saturator on the secondary side. The heat exchanger thus transmits heat from the synthesis gas, also designated as crude gas, flowing into the saturator into the synthesis gas, also designated as mixed gas, flowing out of the saturator. The heat exchanger (also designated as a crude-gas/mixed-gas heat exchanger) thus gives rise to an at least partial heat-side bypass of the saturator. Thereby, the thermodynamic losses of the overall process are kept particularly low due to the heating of the synthesis gas by the crude gas. The fuel-side arrangement of the mixing device upstream of the saturator at the same time ensures that the crude-gas/mixed-gas heat exchanger transmits the heat from the crude gas to a particularly large mass stream. Thus, by virtue of an arrangement of this type, a particularly favorable heat exchange can be achieved, since, under the boundary condition of a constant final temperature, a comparatively large quantity of heat can be transmitted to the mixed gas flowing out of the saturator.
For especially high plant efficiency, in an advantageous development, the crude-gas/mixed-gas heat exchanger is preceded in the fuel line by a crude-gas heat recovery steam generator upstream of the saturator. The crude-gas heat recovery steam generator precools the synthesis gas or crude gas generated in the gasification device. This precooling is beneficial for material reasons. At the same time, the heat extracted from the crude gas can be utilized in an especially beneficial way for steam generation. In steam generation, in a plant designed for the gasification of coal as fossil fuel, a so-called gas quench may be provided, in which so-called quench gas, branched off from the fuel line at a point between the crude-gas/mixed-gas heat exchanger and the saturator, is supplied to the synthesis gas before the latter enters the crude-gas heat recovery steam generator. In an arrangement of this type, the crude-gas mass flow is approximately comparable to the mixed-gas mass flow, so that the mixed gas can be preheated by heat exchange with the crude gas to temperatures of well above three degrees Celsius ( greater than 300xc2x0 C.) under customary operation conditions.
Expediently, a further heat exchanger is connected on the secondary side into the fuel line between the saturator and the combustion chamber. The further heat exchanger can be heated, for example, with a medium-pressure feedwater. In this arrangement, even in the case of only limited cooling of the crude gas, for example because of boundary conditions set by a crude-gas dedusting device, reliable preheating of the mixed gas, along with especially high plant efficiency, is ensured. A concept of this type for mixed-gas preheating is also particularly suitable for a plant that is designed for the gasification of coal as fossil fuel and in which gas quench is not provided or for a plant designed for the gasification of oil as fossil fuel. Particularly in the case of a plant designed for the gasification of coal and without gas quench, the crude-gas mass flow is usually approximately half the mixed-gas mass flow. This limits the mixed-gas preheating by the crude-gas/mixed-gas heat exchanger to a temperature range of about 200xc2x0 C. to 230xc2x0 C. Therefore, in a plant of this type, additional mixed-gas preheating via a further heat exchanger is especially beneficial. The further heat exchanger can be heated with high-pressure feedwater.
Advantages of the invention include, that the crude-gas/mixed-gas heat exchanger, provided in addition to the mixing device connected into the fuel line upstream of the saturator, allows the heat exchanger to have an especially favorable transmission of heat from the crude gas flowing into the saturator to the mixed gas flowing out of the saturator, by bypassing the saturator. Therefore, thermodynamically unfavorable cooling and reheating of the synthesis gas are necessary only to a limited extent, so that the efficiency of the gas and steam turbine plant is especially high.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a gas and steam turbine plant, the invention is nevertheless not intended to be limited to the details shown, because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.